1. Field of the Invention
The present invention relates to a color image processing method and system.
2. Description of the Prior Art
In a prior art color recording apparatus which uses a binary recording technique, an input image data is represented by a binary tone level by a dither matrix or a modified matrix thereof. As a result, in a high resolution area such as a character or symbol area, fine lines are broken by the dither and image quality deteriorates. One resolution method for a monochromatic image or a black-and-white image is shown in "Adaptive Switching of Dispersed and Clustered Halftone Patterns for Bi-Level Image Rendition" reported in SID 77 DIGEST by Kwan Y. Wong of IBM. Two approaches, one by Laplacian gradient and the other by maximum of corner sums are discussed therein. For a monochromatic image, an original image is checked to determine whether it is in a gray level image area or in a high resolution image area, such as a character area, to determine a dither processing or a single threshold processing for binarization.
The prior art method for discriminating the high resolution image area or the gray level image area for the monochromatic image is described below. FIG. 1 shows a configuration shown in Japanese Kokai 58-3374. Image input data 200 is alternately stored in line buffer memories 202 and 203 by positioning switch 201A. In FIG. 1, the memory 202 acts as an input line buffer memory and the memory 203 acts as an output line buffer memory. The memories 202 and 203 are n-line buffer memories. Numeral 204 denotes a block memory for determining whether an n.times.n-pixel area of an original image is a high resolution image data or a gray level image data and is connected either to memory 202 or memory 203 by switch 201B. It stores an n.times.n-pixel data. Numeral 205 denotes a discriminator for discriminating a type of the image data by checking the n.times.n-pixel data of the memory 204.
A maximum value Pmax and a minimum value Pmin of the pixel data in the block memory 204 are determined, and if (Pmax-Pmin).gtoreq.L, it is discriminated that the image in the block is in the high resolution image area and a threshold selection switch 209 is thrown to a position B to select single threshold matrix table 207. If (Pmax-Pmin)&lt;L, it is discriminated that the image is in the gray level and a dither matrix table 206 is selected by an output signal of the discriminator 205. Numeral 208 denotes a comparator which compares threshold data selected by the switch 209 with pixel data from the block memory 204. An output of the comparator 208 is binarized and it is supplied to a binary ON/OFF printer 210 for binary image recording.
However, for a color image, an original image data is usually separated to R (red), G (green) and B (blue) color components by an input device. Thus, if the IBM technique described above is applied to each of the three color signals, discrimination results may differ for each color signal component in an input pixel area under consideration.
If the discrimination results differ for each color signal, it may occur that a print ink quantity C (cyan) for an input R component is converted to a dot pattern by the dither method and a print ink quantity M (magenta) for an input G component is converted to a dot pattern by the single threshold method. As a result, superimposition of colors may differ and a color reproduced may differ from a desired one. Further, fine lines in the C (cyan) component are broken by the dither and image quality deteriorates.